C# slider/trackbar Control using Windows Forms

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Introduction

ColorSlider is a slider/trackbar control written in C# (Windows Form )

This is an alternative to the standard Microsoft Visual Studio trackbar control which is not so flexible, lack basic functionalities and is a little poor in design.

The code is a free interpretation of the original code from Michal Brylka published in the site Code Project.

See https://www.codeproject.com/Articles/17395/Owner-drawn-trackbar-slider

The main enhancements brought by this control are:

  • a less surface
  • the possibility to parametrize the shape of the thumb or to replace it by an image.
  • subdivisions added between main divisions.
  • the text value of the main divisions.
  • many colors parametrization added (ticks, bar, elapsed)
  • the orientation can be horizontal and vertical (starting from the bottom)

Using the code

The control is drawn in the overrided event OnPaint, depending if it is enabled or not, and if the mouse is over it or not.

  • If not enabled, the colors are desaturated.
  • If the mouse is over, the colors are lighten.
  • Else, the colors are those choosen in the property box.

Depending on these colors, the function DrawColorSlider is called and draw everything.

3 rectangles are mainly used to draw the control:

  • barRect is used to draw the bar (Elapsed and remaining)
  • thumbRect is used to draw the thumb.
  • elapsedRect is the rectangle for the elapsed bar (the left of the thumb if the orientation is horizontal)

The elapsed bar is composed of 3 single lines (inner, top and bottom), having each its own color:






e.Graphics.DrawLine(new Pen(elapsedInnerColorPaint, 1f), x1, y1, x2, y2);

top and bottom lines are drawn 1 pixel above or under the inner line.

A vertical line of 3 pixels is added at the beginning to improve the 3D effect.

The rest of the bar is also composed of 3 single lines (inner, top and bottom), having each its own color.

A vertical line of 3 pixels is added at the end to improve the 3D effect.

The thumb is drawn according to whether it is an image or not:

  • Image: e.Graphics.DrawImage(bmp, thumbRect, srceRect, GraphicsUnit.Pixel);
  • Drawn by the control,with a linear gradien e.Graphics.DrawPath(thumbPen, thumbPath);

The ticks and texts are drawn in two nested loops

  • a first loop from 0 to ScaleDivision for the main graduations and texts
  • a nested loop from 0 to ScaleSubDivision for the subdivisions

The offset between each tick is a multiple of W/(nbticks -1) where:

  • W is the width of the bar, minus the width of the thumb, in order that when the thumb is at minimum position or maximum position, the graduation coincide with the middle of the thumb
  • nbticks is the number of graduations including subdivisions: nbticks = 1 + _scaleDivisions * (_scaleSubDivisions + 1);

Properties

Thumb  
ThumbSize The size of the thumb (Width, Height). allowing you to make circles or rectangles
ThumbCustomShape Gets or sets the thumb custom shape. Use ThumbRect property to determine bounding rectangle.
ThumbRoundRectSize Gets or sets the size of the thumb round rectangle edges.
BorderRoundRectSize Gets or sets the size of the border round rect.
DrawSemitransparentThumb Gets or sets a value indicating whether to draw semitransparent thumb.
ThumbImage Gets or sets a specific image used to render the thumb.
   
Appearance  
Orientation Gets or sets the orientation of the Slider(Horizontal or vertical)
DrawFocusRectangle Gets or sets a value indicating whether to draw focus rectangle.
MouseEffects Gets or sets whether mouse entry and exit actions have impact on how control look.
   
Values  
Value Gets or sets the value of Slider
Minimum (0) Gets or sets the minimum value.
Maximum (100) Gets or sets the maximum value.
SmallChange Gets or sets trackbar’s small change. It affects how to behave when directional keys are pressed.
LargeChange Gets or sets trackbar’s large change. It affects how to behave when PageUp/PageDown keys are pressed.
MouseWheelBarPartitions Gets or sets the mouse wheel bar partitions.
   
Colors  
ThumbOuterColor Gets or sets the thumb outer color.
ThumbInnerColor Gets or sets the inner color of the thumb.
ThumbPenColor Gets or sets the color of the thumb pen.
BarInnerColor Gets or sets the inner color of the bar.
BarPenColorTop Gets or sets the top color of the bar
BarPenColorBottom Gets or sets the bottom color of the bar
ElapsedPenColorTop Gets or sets the top color of the elapsed
ElapsedPenColorBottom Gets or sets the bottom color of the elapsed
ElapsedInnerColor Gets or sets the inner color of the elapsed.
TickColor Gets or sets the color of the graduations
   
Preformated colors  
ColorSchema 3 predefined color schemas are proposed (red, green, blue). The colors can be changed manually and they overwrite them.
   
Ticks  
TickStyle Gets or sets where to display the ticks (None, both top-left, bottom-right)
ScaleDivisions Gets or sets the number of intervals between minimum and maximum
ScaleSubDivisions Gets or sets the number of subdivisions between main divisions of graduation
ShowSmallScale Shows or hides subdivisions of graduations.
ShowDivisionsText Show or hide text value of main graduations.

Events

Two events are available:

  • ValueChanged
  • Scroll

Typical usage of ValueChanged event:

private void colorSlider1_ValueChanged(object sender, EventArgs e)
 {
 label1.Text = colorSlider1.Value.ToString();
 }

Points of Interest

This project was developed with Visual Studio version 2017.

So, as you see, nothing very difficult in this control.

You just have to draw lines and calculate precisely where they start and where they end…

This simple control shows that with a few efforts we can design a control with beautiful effects. The difficulty in reality is not technical, but it consists to choose the right assortiment of colors.

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